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The effect of force can be measured using a physical quantity called pressure. It can be defined as the amount of force or thrust acting perpendicularly on a surface of area of one square meter of a body.
Pressure = Thrust (or) Force / Area
ie., P = F/A
The SI unit of pressure is pascal (named after the French scientist Blaise Pascal).
1 pascal = 1 Nm–2
Pressure exerted by a force depends on the magnitude of the force and the area of contact.
The average weight of an elephant is 4000 N. The surface area of the sole of its foot is 0.1m2. Calculate the pressure exerted by one foot of an elephant.
Average weight of the elephant = 4000 N
Weight of one leg = Force exerted by one leg
= 4000/4 = 1000 N
Area of the sole of one foot = 0.1 m2
Pressure = Force/Area
= 1000/0.1 = 10000 N/m2 = 104 Nm-2
Pressure exerted by one leg of the elephant is 10,000 newton on one square metre.
The effect of pressure can be increased by increasing the thrust or by decreasing the surface area of the body. The axe, nail, knife, injection needle, bullet etc. , are having sharp fine edges so as to exert a larger pressure on a smaller area of the body in order to produce maximum effect.
1. More number of wheels are provided for a heavy goods-carrier for decreasing the pressure thereby increasing the area of contact on the road.
2. Broader straps are provided on a back-pack for giving less pressure on the shoulders by providing a larger area of contact with the shoulder.
It is very difficult for us to walk on sand. But, camels can walk easily on it because they have large padded feet, which increase the area of contact with the sandy ground. This reduces the pressure and enables them to walk easily on the sand.
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